An offset of a sensor refers to a characteristic parameter which is caused by non-uniformity in a sensor fabrication process. That is, an offset of a sensor refers to a difference between an ideal output value and a real output value of the sensor when there is no input signal to the sensor.
FIG. 1 illustrates an operation method of a planar hall resistance (PHR) sensor which is one of the Wheatstone bridge type sensors. As shown in FIG. 1, the PHR sensor applies a bias current or voltage between two nodes (between node 1 and node 3 or between node 2 and node 4), and then measures a voltage proportional to an externally input magnetic field between the other nodes (between node 2 and node 4 or between node 1 and node 3).
An amplifier is connected to the PHR sensor as shown in FIG. 1, and an offset of the PHR sensor is calculated by applying only a bias current without applying an external magnetic field (an input magnetic field), and then measuring an output voltage.
FIG. 2 is a view showing four types of real PHR sensors. The PHR sensors illustrated in FIG. 2 may have different patterns of lines for adjusting a line length between nodes. Specifically, type #1 refers to a 1 ring type having a line formed directly between nodes, type #2 refers to a 5 ring type having lines bent between nodes in five times in a zigzag pattern, and type #3 refers to a 11 ring type having lines bent between nodes in 11 times in a zigzag pattern, and type #4 refers to a 17 ring type having lines bent between nodes in 17 times in a zigzag pattern.
FIG. 3 illustrates offset voltages which are measured after sampling 11 real PHR sensors of each type as shown in FIG. 2 and applying a bias current of 1 mA to the real PHR sensors. As shown in FIG. 2, since the offset voltages of the real PHR sensors are not uniform, there is inconvenience that offset voltages should be individually measured at every PHR sensor.
In addition, the offset voltage varies according to a bias current. Accordingly, when the bias current is changed, the offset voltage is also changed and thus the offset voltage should be displayed with the bias current.